Modulation Scheme for Five-Phase Electric Machines With Nonlinear Optimization to Improve Voltage Limit Performance

Five-phase electric machines include an
αβ
-space and a
xy
-space, which should be simultaneously considered when designing the machine controller. In this article, we propose a unique modulation scheme based on the nonlinear optimization to synthesize control voltages in both spaces. The advantage of the proposed scheme is to eliminate the influence of the modulation process in the
xy
-space on that in the
αβ
-space. Thereby, the torque output can be guaranteed first when dc bus voltage is limited. The proposed modulation scheme follows a two-step mechanism. First, the synthesis of
αβ
-space control voltages is guaranteed, and the action time constraints of the basic control voltage vectors are determined. Second, the synthesis of
xy
-space control voltages is realized with an objective function. By minimizing the objective function according to the action time constraints with the Karush–Kuhn–Tucker approach, the optimal action time is calculated, and the duty cycle of the inverter is obtained. The experimental results have been presented to verify the performance improvement of the proposed method.